Bird flu has been invading the brains of mammals. Here’s why

Science News

In spring 2022, a handful of red foxes in Wisconsin were behaving oddly. Veterinary pathologist Betsy Elsmo learned that a local wildlife rehabilitation center was caring for foxes with neurological symptoms like seizures, tremors, uncoordinated movements and lethargy.

But tests for common pathogens like canine distemper virus and rabies that typically cause the symptoms came back negative. Then a red fox kit tested positive for influenza A. This group of viruses includes seasonal flus that cause respiratory disease in people and many other strains that commonly circulate among animals such as waterfowl and other birds.

“I was surprised,” says Elsmo, of the University of Wisconsin–Madison. “And to be honest, at first I kind of wrote it off.”

That is, until a veterinary technician at the rehab center sent Elsmo a study describing cases of avian influenza in red foxes in the Netherlands. Examinations of the Wisconsin kit’s tissues under the microscope revealed lesions in the brain, lung and heart that matched what had been seen in the Netherlands animals. “And I thought, I think it is [bird flu],” she recalls.

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